Arbitrary and pointless limit. Sometimes “no” is quite enough.
The character minimum is there to prevent from spamming, to discourage posts with no meaningful content, to filter out junk replies such as +1, LOL, etc. It is quite effective.
It is an attempt to encourage people to engage in meaningful conversation when responding to posts, rather than just responding to a post with “Yes,” “No,” “This.” If one has something meaningful to say, one will not be bothered by this reasonable minimum character limit (most forums require many more characters). If one needs to post “5 char.” or the like to get around the rule, your post is typically adding nothing.
Perhaps consider the rule an effort to raise Internet based communication a few IQ points.
Of course, it is just a rule a computer can easily apply. The software cannot recognize the rare occasion when a shorter reply is actually truly useful.
Perhaps we should tighten up the maximum character limit as it would encourage the long-winded to calm down a bit. 
Thanks Elk. Makes sense.
Maybe some way to get rid of hyperbole? Or how about redundant hyperbole?